The line must pass through the point (0, 0, 3) and have direction vector (-1, 3, -6). Then x= 0+ (-1)t= -t, y= 0+ 3t= 3t, and z= 3+ (-6)t= 3- 6t work.
In general, the line passing through $(x_0, y_0, z_0)$ with direction vector (A, B, C) has parametric equations $x= x_0+ At$, $y= y_0+ Bt$, and $z= z_0+ Ct.